The present invention generally pertains to image processing. More specifically, the present invention relates to methods and procedures for analyzing biometric image information and generating a corresponding directional field estimate.
Image identification systems have been used in the past, one application being biometric image identification systems. One type of biometric image identification system is a fingerprint identification system. In one example of a fingerprint identification system, a user places the tip of a finger on a scanning surface of a fingerprint image reader device. Each ridge of the epidermis (outer skin) is dotted with sweat glands that produce moisture that, in combination with oily secretions and other substances naturally present on the tip of a finger, enable an image of a fingerprint to be scanned. Alternatively, in some instances, images can be generated from readers that do not rely on the moisture content of the skin to capture an image (e.g., some systems simply capture a picture of print ridge characteristics). Regardless of the precise image collection means, collected image information is commonly compared to a database of stored information for verification, authentication, or some other form of analysis.
Security systems that implement fingerprint identification technology have the potential of being reliable and easy to use. These benefits arise from the fact that the technology does not require a system user to retain any piece of knowledge, such as a password, personal identification number, combination or any other code. Neither must a user possess a card, key or any other physical device to gain access to a secured environment. A fingerprint security authentication key, as opposed to a knowledge or possession based security authentication key, is nearly impossible to lose, steal, or be forgotten.
Development of practical security system applications that incorporate fingerprint image identification technology has been hindered by a general non-repeatability of data from one image scan to another. In particular, physical variations present in the environment of a fingerprint reader device can cause substantial incongruities from one image scan of a fingerprint as compared to a subsequently taken image scan of the same fingerprint. Differences in the temperature, amount of pressure applied to the scanning surface, moisture content of the finger, as well as the effects of medications and differences in blood pressure can all contribute to substantial incongruities from one image scan to another. These and other types of inconsistencies have the potential to throw off image analysis and comparison algorithms, which can lead to inaccurate results.
Accordingly, inconsistency has the potential to hinder the development of fingerprint identification technology applications. Inconsistent data can lead to an unacceptably high number of false acceptances (multiple identifications including matching to wrong individuals) and false rejections (not recognizing an enrolled individual). Security applications that require instantaneous and unsupervised comparisons to be made between a scanned fingerprint image and a database of fingerprint images or fingerprint models often have a low tolerance for inconsistency.
A processing component known to be a part of some image data analysis algorithms is the generation of directional field information, which in the context of fingerprint images includes information pertaining to ridge direction. The accuracy of current methods for estimating directional field information is relatively limited. Known methods can be unreliable and not work well in the context of undesirable but common artifacts such as scratches, cuts and wet or dry spots. Because directional field estimation information is commonly utilized as a processing sub-component of an image analysis system, a limited accuracy in the context of a directional field estimate can compromise the accuracy of the overall image analysis process, thereby contributing to inconsistent overall results.